Various cardiovascular, neurosurgical, pulmonary, and other interventional procedures, including coronary artery bypass grafting, heart valve repair and replacement, septal defect repair, pulmonary thrombectomy, removal of atrial myxoma, patent foramen oval closure, treatment of aneurysms, myocardial drilling, electrophysiological mapping and ablation, angioplasty, atherectomy, correction of congenital defects, and other interventional procedures may require general anesthesia, cardiopulmonary bypass, and arrest of cardiac function. In order to arrest cardiac function, the heart and coronary blood vessels must be isolated from the remainder of the circulatory system. This serves several purposes. First, such isolation facilitates infusion of cardioplegic fluid into the coronary arteries to perfuse the myocardium and paralyze the heart without allowing the cardioplegic fluid to be distributed elsewhere in the patient's circulatory system. Second, such isolation facilitates use of a cardiopulmonary bypass system to maintain circulation of oxygenated blood throughout the circulatory system while the heart is stopped without allowing such blood to reach the coronary arteries and resuscitate the heart. Third, in cardiac procedures, such isolation creates a working space into which the flow of blood and other fluids can be controlled or prevented so as to create an optimum surgical environment.
Circulatory isolation of the heart and coronary blood vessels is usually accomplished by placing a mechanical cross-clamp externally on the ascending aorta downstream of the ostia of the coronary arteries, but upstream of the brachiocephalic artery so that oxygenated blood from the cardiopulmonary bypass system reaches the arms, neck, head, and remainder of the body. Using conventional techniques, the sternum is cut longitudinally (a median sternotomy) thereby providing access between opposing halves of the anterior portion of the rib cage to the heart and other thoracic vessels and organs. Alternatively, a lateral thoracotomy is formed, wherein a large incision is made between two ribs and the ribs are retracted apart. A portion of one or more ribs may be permanently removed to optimize access.
Through this large opening in the chest, a cross-clamp is placed externally on the ascending aorta thereby isolating the heart and coronary arteries from the remainder of the arterial system. Frequently, the aorta must be dissected away from adjacent tissue to facilitate placement of such a cross-clamp.
To arrest cardiac function, a catheter is introduced through the sternotomy or thoracotomy and inserted through a puncture in the aortic wall into the ascending aorta between the cross-clamp and the aortic valve. Cardioplegic fluid is infused through the catheter into the aortic root and coronary arteries to perfuse the myocardium. An additional catheter may be introduced into the coronary sinus for retrograde perfusion of the myocardium with cardioplegic fluid. In addition, the myocardium is sometimes cooled by irrigation with cold saline solution and/or application of ice or cold packs to the outside of the heart. Cardiac contractions will then cease.
In surgical procedures requiring a median sternotomy or other form of gross thoracotomy, the ascending aorta is accessible for placement of an external cross-clamp through the large opening in the chest. However, such open-chest surgery often entails weeks of hospitalization and months of recuperation time as well as pain and trauma suffered by the patient. Moreover, the average mortality rate associated with this type of procedure is about two to fifteen per cent for first-time surgery, and mortality and morbidity are significantly increased for reoperation.
New devices and methods are therefore desired to facilitate the performance of cardiac procedures such as heart valve repair and replacement, coronary artery bypass grafting, and the like, using minimally invasive techniques, eliminating the need for a gross thoracotomy. Such techniques are described in U.S. Pat. No. 5,452,733, and application Ser. No. 08/163,241 filed Dec. 6, 1993, which are assigned to the assignee of the present invention and are incorporated herein by reference. In those applications, methods and devices are described for performing coronary artery bypass grafting, heart valve repair and replacement, and other procedures through small incisions or cannulae positioned in the chest wall, obviating the need for a gross thoracotomy. One technique described for arresting the heart during such procedures involves the use of a catheter which is introduced into a peripheral artery such as a femoral artery and positioned in the ascending aorta. An expandable member at the distal end of the catheter is expanded within the ascending aorta to block blood flow therethrough. Cardioplegic fluid is then be infused into the aortic root and into the coronary arteries through a lumen in the catheter, and/or in a retrograde manner through a catheter positioned in the coronary sinus, paralyzing the myocardium.
While this endovascular technique for arresting the heart provides significant advantages over conventional open-chest techniques, in some circumstances the use of an endovascular device for aortic partitioning may be undesirable. For example, in some cases the patient's femoral arteries and other vessels in which such a device could be introduced may not be suitable for such introduction, due to inadequate vessel diameter, vessel stenosis, vascular injury, or other conditions. In addition, where a number of endovascular cannulae are to be introduced to support cardiopulmonary bypass, retroperfusion of cardioplegic fluid, removal of blood from the heart, and other functions, a suitable arterial location for introduction of an endovascular aortic partitioning device may not be available. Further, it may be desirable to minimize the number of arterial punctures so as to reduce the risk of infection and other complications stemming from such punctures.
The present invention also provides an improved method and apparatus for clamping a patient's internal mammary artery for performing a coronary artery bypass procedure. In order to use a mammary arterial graft in a coronary artery bypass procedure, blood flow through the target mammary artery is temporarily stopped using a removable surgical clamp. In a conventional open-chest procedure, a relatively large, easy to handle clamp is applied by hand or with a forceps directly to the mammary artery through the large opening in the patient's chest provided by a median sternotomy. After the mammary artery is clamped, the mammary artery is ligated and divided at a location downstream from the clamp to create a free end which is connected to the coronary artery. After the grafting is complete, the clamp is removed by the surgeon, typically by hand or with the open forceps, to permit blood to flow through the mammary artery and into the coronary artery downstream of the blockage. As discussed above, gross thoracotomies used in conventional open heart surgery are highly traumatic to the patient and, therefore, new methods of performing surgery on the heart using minimally-invasive techniques have been recently developed. A further application of the present invention is for clamping the internal mammary artery for performing a coronary artery bypass procedure when performing minimally invasive heart surgery.